Method for manufacturing of vehicle armor components requiring severe forming with very high bend angles with very thick gauge product of high strength heat treatable aluminum alloys

ABSTRACT

It has been commonly believed that very thick gauge high strength aluminum alloy product such as AA2139 plate cannot be formed to the required sharp angles to form the highly protective underbody armor for the MRAP vehicles. The present process and method of manufacture provides a means for strategically combining the metallurgical process of manufacturing high strength aluminum alloys and the forming process of V shaped hull to improve the formability of the very thick gauge high strength alloy product so much that even the very thick gauge (thicker than 1 inch) plate can be formed to severe forming angles. This combined process allowed successful manufacturing of high performance V shaped hulls for the Mine Resistant Ambush Protected (MRAP) vehicles.

INTRODUCTION

A Mine Resistant Ambush Protected (MRAP) vehicle is a family of armoredfighting vehicles designed for the U.S. Army and United States MarineCorps with the goal of surviving IED attacks and ambushes—prompted by USdeaths in Iraq.

MRAP vehicles usually have “V” shaped hulls to deflect away anyexplosive forces originating below the vehicle, thereby protecting thevehicle and its passenger compartment. Typically these explosions arefrom land mines, but they can also be IEDs (Improvised ExplosiveDevices).

BACKGROUND

Historically the V shaped hulls are made of welded steel plate, which isvery heavy and added much more weight to the armored vehicles to slowdown its mobility and limit the ammunition and personnel carryingcapacity. The vehicle's weight and size severely limits its mobility offmain roads, in urban areas, and over bridges (reference 1). 72 percentof the world's bridges cannot hold the MRAP. Its heft also restrictsseveral of the vehicles from being transported by C-130 cargo aircraftor the amphibious ships that carry Marine equipment and supplies.

Instead of steel plate armor, it would be more desirable to use aluminumalloy plate to make it lighter. Unfortunately, the traditional aluminumarmor alloys such as AA5083 and AA6061 are not strong enough to provideadequate protection against land mines and IED's. More recentlydeveloped high strength heat treatable aluminum alloys such as AA2139and AA2519 among 2000 series alloys and AA7085 and AA7081 among the 7000series alloys could meet the material property requirement for thevehicle armor components and underbody “V” hull for armored vehicles andMRAPs, respectfully. Recently, a new aluminum alloy, AA2139, has beendeveloped by Cho et al. to provide much improved ballistic and mineblast protection compared to the traditional aluminum alloy based armorplate. The chemistry of the high strength heat treatable aluminum alloysas candidate materials for armor plate applications are listed in theTABLE 1 for AA2139, TABLE 2 for AA2519, TABLE 3 for AA2027, TABLE 4 forAA7085 and TABLE 5 for AA7081.

TABLE 1 Alloy Chemistry of AA2139 Element wt. % Si  0.1 max Fe 0.15 maxCu  4.5-5.5 Mn 0.20-0.6 Mg 0.20-0.8 Cr 0.05 max Zn 0.25 max Ti 0.15 maxV 0.05 max Ag 0.15-0.6

TABLE 2 Alloy Chemistry of AA2519 Element wt. % Si 0.25 max Fe 0.30 maxCu 5.3-6.4 Mn 0.10-0.5  Mg 0.05-0.40 Cr 0.05 max Zn 0.10 max Ti0.01-0.10 V 0.05-0.15 Zr 0.10-0.25

TABLE 3 Alloy Chemistry of AA2027 Element wt. % Si 0.12 max Fe 0.15 maxCu  3.9-4.9 Mn 0.50-1.2 Mg  1.0-1.5 Cr 0.05 max Zn 0.20 max Ti 0.08 Zr0.05-.25

TABLE 4 Alloy Chemistry of AA7085 Element wt. % Si 0.06 max Fe 0.08 maxCu 1.3-2.0 Mn 0.04 max Mg 1.2-1.8 Cr 0.04 max Zn 7.0-8.0 Ti 0.06 max Zr0.06-0.25

TABLE 5 Alloy Chemistry of AA7081 Element wt. % Si 0.12 max Fe 0.15 maxCu 1.2-1.8 Mn 0.25 max Mg 1.8-2.2 Cr 0.04 max Zn 6.9-7.5 Ti 0.06 max Zr0.06-0.25

The conventional manufacturing method of the “V” hull shaped underbodyarmor utilizing high strength alloys consists of welding two or morenumber of flat plate together by conventional welding techniques such asGas Metal Arc Welding (GMAC) or Friction Stir welding. Suchmanufacturing processes increase the cost and lower the materialproperties drastically. For example, GMAC process on high strength, highballistic performance aluminum alloys would lower the strength of thewelded plate by as much as 70% compared to the original materialproperties prior to welding. Friction Stir welding process couldsomewhat improve the post-welding strength compared to that of GMACprocess at a much higher cost and gauge limitations. Yet the post-weldmechanical properties after Friction Stir Welding (FSW) process is stilllower by as much as 35% compared to the original strength of the alloyprior to welding. Therefore, the “V” shaped hull manufacturing processconsists of welding processes (GMAW and/or FSW) would degrade thematerial properties and severely degrade the protection capabilityprovided by the V shaped underbody armor against the land mines andIEDs, which MRAPs are designed for.

SUMMARY OF THE INVENTION

This application incorporates by reference U.S. Pat. No. 7,229,508, U.S.Pat. No. 6,972,110 and PCT Application Publication No. WO 2004/090185A1all of which are incorporated by reference herein in their entirety.Reference to documents made in the specification is intended to resultin such patents or literature cited are expressly incorporated herein byreference, including any patents or other literature references citedwithin such documents as if fully set forth in this specification.

One of the solution to avoid the over weight of MRAP vehicles due to theover weight of the underbody armor of the “V” shape hull is to find amanufacturing process of low weight, high performance underbody armorutilizing high strength, high ballistic performance aluminum alloys suchas high strength 2000 series and 7000 series heat treatable alloys. Thepreferred solution is to avoid any welding processes which degrade theproperties of the aluminum alloys significantly. This can be achieved bymanufacturing the “V” shaped hull by forming instead of welding process.However, “V” shaped hulls for MRAP underbody armor based on highstrength aluminum alloys via. forming process without welding have notbeen available to date because of the following reasons.

1) Highly protective Underbody armor for MRAP vehicles requires verythick gauge aluminum alloy plate2) Forming process for highly protective underbody armor for MRAPrequires severe angle of bend forming to meet the geometry requirement.3) Forming process of very thick gauge material to sharp bend angleswould require very high formability of the material4) High strength, high ballistic performance aluminum based alloys donot have high formability.

It has been commonly believed that very thick gauge high strengthaluminum alloy product such as AA2139 plate cannot be formed to therequired sharp angles to form the highly protective underbody armor forthe MRAP vehicles. However, it was unexpectedly discovered thatstrategically combining the metallurgical process of manufacturing highstrength aluminum alloys and the forming process of V shaped hull couldimprove the formability of the very thick gauge high strength alloyproduct so much that even the very thick gauge (thicker than 1 inch)plate can be formed to severe forming angles. This combined processallowed successful manufacturing of high performance V shaped hulls forthe Mine Resistant Ambush Protected (MRAP) vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had uponreference to the following description in conjunction with theaccompanying drawings in which like numerals refer to like partsthroughout the several views and wherein:

FIG. 1. Picture of the 2.5 inch thick 2139-T8 temper plate after a bendforming attempt. The plate was fractured at bend angle of 160 degrees;

FIG. 2; A schematic diagram of vehicle armor component of 2.5 inch thickAA2139 alloy plate which requires bend angle of 144 degrees, 140degrees, and 135 degrees;

FIG. 3; A picture of the successfully formed a vehicle armor componentof 2.5 inch thick AA2139 alloy plate by following the invented formingprocess. This part requires bend angle of 144 degrees, 140 degrees, and135 degrees as shown in FIG. 2;

FIG. 4; A schematic diagram of vehicle armor component of 2.5 inch thickAA2139 alloy plate which requires bend angle of 135 degrees, 130degrees, and 125 degrees;

FIG. 5; A picture of the successfully formed a vehicle armor componentof 2.5 inch thick AA2139 alloy plate by following the invented formingprocedure. This part requires bend angles of 135 degrees, 130 degrees,and 125 degrees as shown in the FIG. 4; and

FIG. 6; One example of the underbody armor component design for armoredvehicles which require 125 degree and 140 degree bending of 2.5 inchthick gauge plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

By strategically combining metallurgical process of manufacturing highstrength heat treatable alloys and bend forming of very thick gauge workpiece, high strength heat treatable alloys can be formed into variousarmor components for armored vehicles even for the parts requiring verythick gauge plate and bend forming of sharp angles.

For very thick plate of 2000 series aluminum alloys such as 1 inch to 6inch thick gauge 2139 alloy plate and 2519 alloy plate can be solutionheat treated at 960° F.-980° F. and cold water quench for conditioningthe work piece to be ready for forming operation. After forming the workpiece to the final shape, the work piece can be age hardened to meethigh ballistic and blast resistance for the armored vehicles. A coldstretch of the work piece by a small amount right after the solutionheat treatment can be a part of the conditioning the work piece forforming operation. This would further improve the final mechanicalproperties and minimize the residual stress of the formed and agehardened work piece in the final temper condition.

For very thick plate of 7000 series aluminum alloys such as 1 inch to 6inch thick gauge 7085 alloy plate and 7081 alloy alloy plate can besolution heat treated at 860° F.-880° F. and cold water quenched tocondition the work piece to be ready for forming operation. Afterforming the work piece to the final shape, the work piece can be agehardened to meet high ballistic and blast resistance for the armoredvehicles. A cold stretch of the work piece by a small amount right afterthe solution heat treatment can be a part of the conditioning the workpiece for forming operation. This would further improve the finalmechanical properties and minimize the residual stress of the formed andage hardened work piece in the final temper condition.

Example 1

To examine the forming capability of high strength armor alloy 2139-T8plate, a test sample of a 2.5 inch thick×5 inch wide×18″ long sampleplate was sawed from a commercially produced large parent plate of2139-T8 plate delivered from the plate rolling mill of the Alcan RolledProducts LLC, located at Ravenswood W. Va. USA. The formability of the2.5 inch thick 2139-T8 flat plate (180 degree) was formed by a breakforming press with the 16 inch apart two supporting points in the bottomdie and the 4 inch radius of the top die blade. The goal was to bend theplate to at least 144 degrees to meet the geometry requirement for thecurrent design of the V shaped hull of an MRAP vehicle. However, theformability of the 2139-T8 plate was not robust enough to achieve therequired amount of bending. As a result, the sample plate was fracturedat the bending angle of 160 degrees as shown in the FIG. 1. This testresult confirmed that the formability of very thick gauge 2139-T8 plateis not robust enough to produce the V shaped very thick gauge highstrength aluminum alloy hull of an MRAP. It is generally known in theprofessional community skilled in the art that very thick gauge highstrength heat treatable aluminum alloy plate are not formable.

Example 2

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenizedat 980 F for 24 hours and hot rolled to 2.5 inch gauge plate in thetemperature range of 800 F-900 F and subsequently followed by solutionheat treated at 980 F for 3 hours and cold water quenched. After coldwater quench, the plate was cold stretched by 3 percent permanent set tocondition the plate to be formed by severe bending. The plate was formedto an armor component requiring of three bend angles of 144 degrees, 140degrees and 135 degrees, to make a desirable geometry to make armoredvehicle components. The schematic diagram of the intended geometry isshown in FIG. 2. FIG. 3 shows the picture of the component successfullyformed to meet the geometry shown in FIG. 2. The plate is now ready tobe aged to the high strength mechanical property requirement by ageprocess known in the art. The most typical age process is to heat up thework piece to 320° F. and soak at the temperature for 36 hours. Avariation of thermal procedures could be utilized at the temperaturerange of 250°-380° F. for durations selected appropriately to thetemperatures selected.

Example 3

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenizedat 980 F and hot rolled to 2.5 inch gauge plate in the temperature rangeof 800 F-900 F and subsequently followed by solution heat treated at 980F for 3 hours and cold water quenched. After cold water quench, theplate was cold stretched by 3 percent permanent set to condition theplate to achieve high strength after final heat treatment, and yet beformed by severe bending. The plate was formed to an armor componentrequiring of three bend angles of 135 degrees, 130 degrees and 125degrees, to make a desirable geometry to make armored vehiclecomponents. The schematic diagram of the intended geometry is shown inFIG. 4. FIG. 5 shows the picture of the component successfully formed tomeet the geometry shown in FIG. 4. The plate is now ready to be aged tothe high strength mechanical property requirement by age process knownin the art. The most typical age process is to heat up the work piece to320° F. and soak at the temperature for 12-48 hours. A variation ofthermal procedures could be utilized at the temperature range of250°-380° F. for durations selected appropriately to the temperaturesselected.

Example 4

FIG. 6 shows one example of the underbody armor component design forarmored vehicles which require 125 degrees and 140 degrees bending of2.5 inch thick gauge plate.

Various geometries of highly effective armor components with very thickgauge high strength aluminum alloys can be manufactured by utilizing theinvented procedure of combination of material processing steps andforming processes as described above.

Example 5

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenizedat 980 F and hot rolled to 2.0 inch gauge plate in the temperature rangeof 800 F-900 F and subsequently followed by solution heat treated at 980F for 3 hours and cold water quenched. After cold water quench, theplate was cold stretched by 3 percent permanent set to condition theplate to achieve high strength after final heat treatment, and yet beformed by severe bending. The plate was formed to an armor componentrequiring of three bend angles of 140 degrees, 160 degrees and 160degrees, to make a desirable geometry to make armored vehiclecomponents. The formed parts are age strengthened at 320 F for 24 hours.

Performance Characteristics of the Formed Underbody Armor

-   -   1. The mechanical properties of the formed underbody armor after        final heat treatment are different from those of flat plate        armor. The three bent areas in the formed underbody armor are        very high in strength due to the high level of cold work (as        high as 22%) and provide extremely rigid structural integrity of        the overall armor against the blast force, and the flat portion        between the bent areas are moderately high in strength due to        the moderate level of cold work (nominally 3%) and provide high        rupture resistance with very high fracture toughness. Such a        unique combination of mechanical properties enhances the        geometrical advantage of formed underbody armor as described in        above.    -   2. The examples of the mechanical properties are listed below        from the sample material processed by the identical        manufacturing procedures as the above manufacturing process        specifications.        -   a. Mechanical Properties of sample plate representative of            the flat portion between the bent area having nominal 3%            cold work

UTS (ksi) TYS (ksi) El (%) K1c (ksi-√inch) 68.5 63.5 16 58.1 68.0 63.316 54.2

-   -   -   b. Mechanical Properties of the sample plate having 18% cold            work, representative of the bent area

UTS (ksi) TYS (ksi) El (%) K1c (ksi-√inch) 75.6 70.7 10 N.A.

These are very desirable combination of mechanical properties to ensuresuperior performance for armor application compared to the mechanicalproperties of flat rolled plate of 2139-T8 temper plate per SAE-AMSSpecification No. 4468 (see below)

Mechanical Properties (L Direction) of 2139-T8 Flat Plate per SAE-AMSSpec 4468

UTS (ksi) TYS (ksi) El (%) K1c (ksi-√inch) 66 62 9 35

MODIFICATIONS

Specific compositions, methods, or embodiments discussed are intended tobe only illustrative of the invention disclosed by this specification.Variation on these compositions, methods, or embodiments are readilyapparent to a person of skill in the art based upon the teachings ofthis specification and are therefore intended to be included as part ofthe inventions disclosed herein.

Reference to documents made in the specification is intended to resultin such patents or literature cited are expressly incorporated herein byreference, including any patents or other literature references citedwithin such documents as if fully set forth in this specification.

The foregoing detailed description is given primarily for clearness ofunderstanding and no unnecessary limitations are to be understoodtherefrom, for modification will become obvious to those skilled in theart upon reading this disclosure and may be made upon departing from thespirit of the invention and scope of the appended claims. Accordingly,this invention is not intended to be limited by the specificexemplifications presented herein above. Rather, what is intended to becovered is within the spirit and scope of the appended claims.

1. A method of manufacturing highly effective vehicle armor with verythick gauge high strength heat treatable aluminum alloys bystrategically combining forming process and the metallurgical process ofthe alloy a) Thick gauge aluminum alloy products comprised of thethickness range of from 1 inch to 6 inch thick product b) High strengthheat treatable aluminum alloys comprised of; i) high strength 2000series aluminum alloys such as, but not limited to, AA2139, AA2027, andAA 2519 ii) high strength 7000 series aluminum alloys such as, but notlimited to, AA7085 and AA7081 c) forming process requires solution heattreatment of the work piece at the solutionization temperature andquench the work piece to room temperature to condition the work piece tobe capable of receiving severe forming process by bending or bending andstretching at various bending angles more severe than 160 degrees ofbending angle to meet the geometry requirement of the vehicle armorcomponent d) If desired, a forming process can add a cold stretch by asmall amount after quench the work piece to further improve the materialproperties prior to forming the work piece. e) The formed armorcomponents can be aged to increase the strength of the material to takeadvantage of age hardening characteristics of heat treatable aluminumalloys.
 2. Forming process according to the claim 1, wherein forming thework piece immediately after solution heat treatment and quench step tomaximize the formability during bend forming or stretch and bend formingprocedure. The solution heat treatment for high strength 2000 seriesalloys can be conducted at the temperature range of 960° F. and 980° F.for the durations to be adjusted to the thickness of the work piece. Thesolution heat treatment for high strength 7000 series alloys can beconducted at the temperature range of 860° F. and 880° F. for thedurations to be adjusted to the thickness of the work piece.
 3. Formingprocess according to the claim 1, wherein forming the work piece aftersolution heat treatment and quench step to maximize the formabilityduring bend forming or stretch and bend forming procedure. For verythick plate of 2000 series aluminum alloys such as 1 inch to 6 inchthick gauge 2139 alloy plate and 2519 alloy plate can be solution heattreated at 960° F.-980° F. for the duration of 30 minutes to 6 hoursdepending on the thickness of the work piece and cold water quench forconditioning the work piece to be ready for forming operation. For 2.5inch thick work piece, 2-4 hours of heat treatment at the temperaturearrange of 960° F.-980° F. would be most preferred After forming thework piece to the final shape, the work piece can be age hardened tomeet high ballistic and blast resistance for the armored vehicles. Agehardening can be conducted at the temperature range of 250-380° F. forthe duration of 6 hours to 72 hours depending on the actual agetemperatures selected. This age process can be further modified ifrequired such as need to compensate the limitation of equipmentlimitations to achieve the final age processing effect. A cold stretchof the work piece by a small amount right after the solution heattreatment can be a part of the conditioning the work piece for formingoperation. This would further improve the final mechanical propertiesand minimize the residual stress of the formed and age hardened workpiece in the final temper condition.
 4. Forming process according to theclaim 1, wherein forming the work piece after solution heat treatmentand quench step to maximize the formability during bend forming orstretch and bend forming procedure. For very thick plate of 7000 seriesaluminum alloys such as 1 inch to 6 inch thick gauge 7085 alloy plateand 7081 alloy alloy plate can be solution heat treated at 860° F.-880°F. and cold water quenched to condition the work piece to be ready forforming operation. After forming the work piece to the final shape, thework piece can be age hardened to meet high ballistic and blastresistance for the armored vehicles. A cold stretch of the work piece bya small amount right after the solution heat treatment can be a part ofthe conditioning the work piece for forming operation. This wouldfurther improve the final mechanical properties and minimize theresidual stress of the formed and age hardened work piece in the finaltemper condition.